There are many 3rd party DWF products. Some of the developers of these products are Autodesk DWF Partners. Although becoming a DWF Partner is not required to be able to program independently with DWF, a question I sometimes get asked is "How does a company become a DWF partner?"
A potential partner starts by visiting http://www.autodesk.com/dwf-developers. There they find developer tools, code samples, a list of other 3rd party vendors, and resources. The site is divided into sections:
Create Your Own Application
These sections are intended for C++ programmers who wish to download the free Autodesk DWF Toolkit and build their own application. The Autodesk DWF Toolkit can be downloaded at http://www.autodesk.com/dwftoolkit.
Embed DWF Files into Applications
These sections are intended for Autodesk DWF Viewer or Autodesk Design Review users who have DWF files and wish to integrate them into HTML pages or Microsoft Office documents.
Integrate Our ActiveX Control
Autodesk recently formalized the DWF partner program as part of the Autodesk Developer Network (ADN). Members of the DWF Partner program get all the benefits that come with membership in the ADN and more, including access to the latest Autodesk design technologies and direct support from Autodesk. When developers join ADN and have products that they would like to market, they request an evaluation. If a product meets Autodesk's evaluation criteria, the company is invited to join the DWF Partner program. Once they become an official DWF Partner, they receive access to marketing information that helps them highlight their DWF-based products and partner status. Autodesk promotes the company and its DWF-based products in the DWF Center on http://www.autodesk.com/dwf-partners.